During the fall semester spent at the Italian Academy , cosponsored by the Earth and Environmental Engineering Department of Columbia University of New York, I worked on the research project ‘ Climate changes from decade to century: flood/drought dynamics’. Such a research project involves different partners and Institutions , namely Columbia University (USA) , University of Rome ‘ La Sapienza’(Italy) , National Research Center (CNR-Italy), Institute of Numerical Model (Russian Science Academy), University of Tuscia Italy). The research goal is to produce scientifically sound scenarios of flood and drought risk in N. America and Europe and their projected changes under IPCC scenarios. A novel integrated modelling approach is used to address this issue. The approach entails integration of analyses from a low order dynamical systems model, a medium resolution current ocean-atmosphere GCM, and statistical tools for connecting atmospheric moisture transport and extreme precipitation incidence to the underlying low frequency climate state. A low order model explores the interactions of the key natural modes of ocean-atmosphere variability and their interaction with the mid-latitude atmosphere. The CGM model INMCM3.0 (Volodin & Diansky 2006) allows to simulate planetary climatic conditions for long periods of time under current conditions and under enhanced greenhouse gases conditions. However, given its complexity only a limited number of ensemble runs can typically be performed for a fixed set of parameters. Thus, its use is complementary to the low order models where substantial exploration of the parameters and the associated regimes can be done. In the Fall semester spent in the Italian Academy the research has been addressed to study: - the organization and evolution of climate extremes in the mid-latitude as they are influenced by low-frequency climate modes associated with ocean-atmosphere interactions; specifically such influences have been explored by using observations and low-order models. - precipitation extremes simulated by the medium resolution GCM ( INMCM3.0) as are analyzed for the Mediterranean region. The main findings of the study are extensively discussed in the paper ‘Surface Temperature Gradient and their relation to Mid-latitude Circulation Dynamics & Interannual Precipitation variability: Trends and links to Enso in Observations and Low-order Climate Models ’ by C. Karamperidou, F. Cioffi & U. Lall, and in the two presentations at the AGU2010 Fall Conference , namely (a) ‘"Northern Hemisphere Meridional and Zonal Temperature Gradients and their Relation to Hydrologic Extremes at Mid-latitudes: Trends, Variability and Link to Climate Modes in Observations and Simulations" , by C. Karamperidou, U. Lall & F. Cioffi ; (b) GCM Projections of Precipitation Extremes in the Mediterranean: Changes and Low frequency Characteristics by F. Cioffi ; U. Lall , E. Volodin , C. Karamperidou , R. Purini . These findings are summarized in the following. The analysis of rainfall patterns under global warming shows an increase of rainfall extremes in both frequency and intensity in northern Europe and a decrease in most of the Mediterranean. In the latter region an increase of dry conditions is also observed. The change in the rainfall patterns can be explained by a northward shift of the North Atlantic winter storm track that is one of the main factors in determining moisture and heat transport associated with extreme hydrological events. It depends on how the jet stream dynamics are modulated by large scale ocean-land boundary conditions which depend in turn on both the state of evolution of the known inter-annual and multi-decadal natural variability ( e.g. El Nino-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)) and on changes in meridional and zonal surface temperature gradients ( Equator- Pole gradient (EPG) and Ocean-Land contrast ( OLC), respectively). From the 20th century observations is emerged that different combinations of EPG and OLC are associated with precipitation anomalies at mid-latitudes as Mediterranean and European regions. The Northward shift of the North Atlantic storm track and the associated rainfall patterns are related to a reduction of both EPG and OLC as a consequence of anthropogenic forcing.
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